This invention relates generally to the conversion of polymer resin to molten form for use in a downstream applicator such as a meltblowing die, a spunbond die, an adhesive applicator die, a mold die, and the like. In one aspect the invention relates to a system for delivering pressurized polymer melt to an extrusion die using a fully integrated system. In a specific aspect, the invention relates to a polymer melt delivery system for use in meltblowing.
In many applications involving the use of molten polymer, the polymer resin must not only be melted but must also be delivered to a die under pressure at a controlled rate and temperature. For example, in the production of meltblown products, resin is processed through an extruder, which melts the polymer and delivers it to a die at typical temperatures of between about 400.degree. F. and 800.degree. F. and pressures up to 700 psi. The meltblowing die comprises a row of side-by-side orifices flanked by air passages. The molten resin is extruded through the orifices forming fibers, which are stretched and attenuated by sheets of hot air discharging from the air passages. The microsized fibers are collected on a drum or conveyor in the form of entangled fibers forming a nonwoven web or may be deposited on a substrate. In some meltblowing systems, a gear pump is positioned between the extruder and the die to deliver a metered amount of molten polymer to the die.
Another process in which the present invention has application is in the spunbond operations. In these operations, the molten resin is delivered by the extruder through a spunbond die which forms long generally continuous fibers and differs from the meltblowing operations by the absence of attenuating air streams. The diameters of spunbond fibers are generally much larger than meltblown fibers.
The present invention also has application in the spray application of molten coatings and adhesives. In this process, molten polymer coating or adhesive is applied to a substrate by the use of air extrusion die which may include an air assembly. This process may be considered a meltblowing process since air is used to stretch and attenuate the polymer streams as they discharge from the die orifices.
These processes all involve the extrusion of a polymer melt through a die, but generally require different polymers or different polymer properties.
In all of these applications, there is a need for a simple, efficient system for delivering the polymer melt at controlled rates, pressures, and temperatures. The conventional delivery systems have involved the use of long extruder screws (L/D in the order of 30/1) with close tolerance. The close tolerance between the auger screw and the screw barrel shears the polymer and generates heat which assists in melting the polymer. In some applications, gear pumps are used in series with the extruder. The conventional polymer delivery systems are an arrangement of separate parts (e.g. extruder and gear pump) which are generally limited to the available designs and structures. Such systems do not represent fully integrated systems and therefore must be provided with separate controls, prime movers, heaters, etc.